A washing machine is known to comprise a washing tank intended to contain the washing or rinsing liquid therein, which houses a laundry-loading basket rotating within the tank under the action of motor means. The tank is a body of a generally cylindrical shape, with a longitudinal axis, made of stainless steel or plastic, with a side wall extending along the longitudinal axis, a rear wall and a front wall transversal to the longitudinal axis, and an aperture in the front wall, in those washing machines of the front loading type, or on top of the side wall, in those washing machines of the top loading type, providing access to the inside of the tank. The basket is a mainly cylindrical body made of stainless steel, having a constant diameter along its longitudinal axis, which coincides with the longitudinal axis of the tank and acts as the rotation axis of the basket within the tank. It is also provided with a side wall extending along the axis, a rear wall and a front wall transversal to the axis, and an aperture, either in the front wall or side wall, being arranged such as to match the aperture in the tank, in order to provide access therein for loading and unloading the laundry. The tank axis, and accordingly the basket rotation axis, is normally horizontal; however, washing machines of the front loading type exist in which the tank axis, and accordingly the basket rotation axis, is biased relative to the horizontal axis, such that the tank and basket front walls are at a higher level than the respective bottom walls. Within the basket side wall there are also provided holes such that the washing or rinsing liquid contained in the tank may pass into the basket such that the laundry within the basket is wet by this liquid.
Upon operation, washing or rinsing liquid is supplied to the tank. The washing or rinsing liquid, which accumulates by gravity on the bottom of the tank, penetrates within the basket through the holes provided within the side wall thereof. The laundry contained in the basket is thereby wet by the washing or rinsing liquid obviously, since the surface of the washing or rinsing liquid arranges itself parallel to the ground, i.e. is substantially horizontal, in those washing machines with horizontal axis tank, and accordingly basket, the washing liquid level is constant within the basket all along the axis of the basket itself. Furthermore, according to the widespread trend of reducing the amount of washing liquid employed (to limit water consumption, electric power for water-heating purposes, and detergent consumption), this level is generally low. This makes it difficult to suitably wet all the laundry as desired, and sometimes it requires to provide water recirculation circuits within the washing machine with spraying nozzles placed in the basket.
On the other hand, in those washing machines with biased axis tank, the level of washing liquid in the basket is not the same all along the basket axis, and an accumulation of liquid is found at the lowermost basket area, in the proximity of the rear wall.
The basket rotating within the tank, particularly upon spinning, entails eccentric oscillations of the basket due to an unperfectly even distribution of the laundry contained therein. To avoid that these oscillations may cause the basket to hit the tank, suitable minimum distances are required between the basket and the washing tank.
On the one hand, said minimum distances entail the arrangement of an additional water volume outside the basket, which is therefore not used, and on the other hand the reduction of the basket inner volume with the size of the washing tank being equal.
To increase the volume within the basket, the use of truncated-cone shaped baskets has been suggested, the front diameter of which (away from the support point) is smaller than the rear diameter (at the support cross frame fixed to the basket rear wall), such that the basket has a small dimension only in the area away from the support point, where the width of deformations and vibrations is the greatest.
This solution has the drawback that the centrifugal force acting on the laundry and the basket side wall deforms the latter outwardly with a barrel-shape and that, in the central area of the basket-tank unit, the opening between the washing tank and the basket must be increased by the deformation value of the side wall.
Furthermore, the conical bias of the side wall causes the laundry to be deeply immersed into the washing liquid only at the basket rear wall, the immersion depth rapidly decreasing towards the basket front wall.
Finally, the taper of the basket causes the side wall thereof to be biased relative to the rotation axis, which favours a displacement (axial, at first) of the laundry upon spinning. This displacement of the laundry is not desired, since it entails changes and unbalancing of the mass and inertia distribution of the loaded basket, which in turn increase the oscillations of the basket.